Fix various sources of mutation instead of copying in k8s filter merging code
Fix various sources of mutation instead of copying in k8s filter merging code

This was causing a large number of repeated appending of the same option group

alban/scope,alban/scope,paulbellamy/scope,weaveworks/scope,alban/scope,paulbellamy/scope,paulbellamy/scope,alban/scope,weaveworks/scope,kinvolk/scope,kinvolk/scope,kinvolk/scope,weaveworks/scope,weaveworks/scope,kinvolk/scope,kinvolk/scope,alban/scope,paulbellamy/scope,paulbellamy/scope,weaveworks/scope,alban/scope,weaveworks/scope,kinvolk/scope,paulbellamy/scope